One-component thermosetting coating composition

ABSTRACT

A one-component thermosetting coating composition containing of one or more chemically setting binders, at least one curing or crosslinking agent, and one or more toughening substances, the composition being semisolid and tackfree at temperatures &lt;50° C., wherein the chemically setting binders have an average molecular weight (M w ) of between 500 and 250,000, a melting point of more than 50° C., a glass transition temperature of more than 20° C. and cure fully at temperatures in the range from 80 to 250° C. and in doing so reach at least 10% of the final strength within 15 seconds, wherein the binders have epoxide groups or ethylenically unsaturated groups as reactive groups, wherein the toughening substance is selected from the group consisting of butadiene-acrylonitrile copolymers having terminal carboxyl, epoxide, amino or ethylenically unsaturated groups or are highly branched aliphatic hydrocarbon epoxides, wherein at the least one curing or crosslinking agent is a metal complex of the general formula M(SR) x  B z  in which M=a metal ion, 
     L=a ligand, 
     SR=an acid radical ion, 
     B=a Lewis Base, 
     x=a number from 1 to 8 and 
     z=a number from 7 to 8, and 
     wherein the composition may contain further additives, if desired.

The invention relates to thermosetting coating compositions for treatingsurfaces consisting of different materials with a multifunctional,corrosion-, abrasion- and wear-resistant film or layer of adhesive whichis tack-free at temperatures <80° C. and can be activated by means ofenergy.

Fastening elements which can be used to hold and/or fastenconstructional and functional components on supporting substrates areadequately known. To fasten them to supporting substrates, use ispreferably made of joining techniques having a mechanical and/orphysical action, with all of the disadvantages associated therewith.

In the course of producing a mechanically effective fastening, thesupport materials are damaged by the making of punch holes and/or drillholes. In order, then, to ensure the same load-bearing capacity of thedamaged material, it must be made thicker, which is often technicallyimpracticable and uneconomical.

The physical joining techniques, on the other hand, are based preferablyon various types of welding and soldering, requiring operation at veryhigh temperatures. In the field of fastening, the physical joiningmethods can only be employed when the materials to be united possesssufficiently high and good properties of electrical and/or thermalconductivity. In principle, this is only the case with metal materialcombinations.

Despite an extremely high level of development in application, in thefield of joining and fastening an economic advantage is provided bywelding and soldering only, primarily, since it is possible to fastenelements with short cycle times. From a technical and qualitystandpoint, however, it is the disadvantages which predominate in thecase of the physical joining techniques, and, moreover, they have anadverse effect on the mercantile results. Depending on the particulartechniques and on the metal material combinations, these disadvantagesare, inter alia, as follows:

structural changes undergone by the metal materials in the weld seam andits vicinity as a result of heating;

reduction in the strength values as a result of structural changes;

appearance of stresses in the materials as a result of nonuniformheating, some of which stresses may lead to cracks;

glassy welding sites

slag inclusions

seam not sufficiently welded through (notch effect and fracture risk)

leaky weld seams

holes in the seam

parts to be joined cannot be united by this means when they consist ofdifferent materials

relatively low breakaway torques in the case of welded or solderedfastening elements.

These and other disadvantages are in a causal relationship with theappearance of corrosion sources and/or possible instances of damage tothe anticorrosion layers present on the metal material combinationsfollowing the use of mechanical and/or physical joining methods. Thesesources of corrosion risk can be reduced or eliminated only by means oftime-consuming and cost-intensive reworking, assuming they arerecognized. In addition, such combinations of materials are subject toeven greater restrictions when these conventional joining techniques areemployed, which in turn have an adverse economic effect.

In the processing of thermoplastics, welding is likewise used to producesimple bonds. For fastening, however, physical joining methods are of noimportance in the joining of thermoplastic material combinations, sincethermoplastics possess a series of adverse properties, such as creeps,low thermal stability and, possibly, the migration of plasticizingingredients, for example.

In recent years there has been no lack of efforts in the field offastening to eliminate the disadvantages of the mechanical and/orphysical joining methods by means of conventional adhesive technology.In a few areas, these efforts have led to partial success; in otherwords, the fastening elements have been bonded to a substrate by meansof physically or chemically setting adhesives, for which purposecustomary commercial products have been employed.

In a few specific applications such adhesive fastenings may indeed beuseful; however, they are unsuitable for a production systemincorporating adhesive bonding and fastening. This is because theconventional adhesive systems possess a large number of disadvantages inthis respect, including the following:

long evaporation, drying and setting times in the case of aqueous and/orsolvent-containing, physically setting adhesive systems

long curing times in the case of reactive adhesive systems

low thermal stability and creep resistance in the case of thermoplasticbackbone binders, including the physically setting hot-melt adhesives.

Even by means of physically setting and moisture-curing hot-meltadhesives it is not possible to obtain any satisfactory results.Although it is possible with the physically setting hot-melt adhesivesto treat fastening elements, the films or layers of adhesive producedtherewith are--as a result of their thermoplastic properties--notthermally stable and creep-resistant.

In the case of the moisture-curing hot-melt adhesives a furtherdisadvantage is that the fastening elements treated therewith must bepacked individually in order to protect them against moisture, forexample from the air. They are consequently unsuitable for treatingmass-produced goods. Moreover, these moisture-curing adhesives have thedisadvantage that they require from 12 to 72 hours for full curing. (Seeinter alia R. M. Evans "Polyurethane Sealants", Technomic Publishing,PA, USA, 1993.)

Attempts have also been made to solve the fastening problems by means ofpressure-sensitive adhesives. For example, French Patent 2 542 829describes a fastening element which is provided on the joining surfacewith a double-sided adhesive tape. In its before-use state the layer ofpressure-sensitive adhesive is covered with an abhesive protective film.

Pressure-sensitive adhesives and self-adhesive articles producedtherewith are unsuitable, however, for structural joining and fasteningeven on account of the fact that, as a result of the "micro-Brownian"molecular motion which is permanently present in the layer ofpressure-sensitive adhesive, there is, primarily, only tack at theinterface with the supporting substrate, and there is no adhesion.Moreover, as a result of the "micro-Brownian molecular motion"permanently present, pressure-sensitive adhesives are subject to creep,especially on pore-free substrates. It is to this motion that the personskilled in the art, among others, attributes the self-adhesiveproperties. For this reason alone the pressure-sensitive adhesives areentirely unsuitable for the treatment of fastening elements, since inthe case of application they are unable to develop any permanentadhesion, especially for structural adhesive bonds with a supportmaterial. Similar problems have become known from the practical use ofsimple self-adhesive functional components such as picture hooks.

Recent times have seen the presentation of innovative reaction hot-meltadhesives, which are suitable in particular for the structural bondingof metal automotive components. With these novel adhesives it is indeedpossible, partially, to achieve certain critical adhesion parameters inthe case of specific cases of fastening in assembly, but they arenevertheless unsuitable for the treatment of fastening elements onaccount of the fact, inter alia, that they

possess at room temperature a tacky, pastelike to semisolid aggregatestate and in some cases flow and creep

require long initial curing and through-curing times at hightemperatures, for example ≦5 minutes/220° C., and therefore

are unsuitable for the prior treatment of mass-produced goods--such asfastening elements--and

are unsuitable for overhead mounting and wall mounting.

Consequently, they can be employed in a production system incorporatingadhesive bonding only in combination with spot welding.

For production-line manufacturing, where within short periods it isnecessary to mount and to fasten a large number (for example from 100 to500 pieces) of fastening elements by hand and/or, in particular, bymeans of robot technology, as is the case, inter alia, in vehicleconstruction, the industry and commercial economy have long soughtbetter, alternative and innovative solutions to replace physical joiningin the field of fastening. However, other grounds for the demand foralternative joining methods are the limitation of the physical joiningtechniques to metal material combinations, and the potential hazardspresent. At the same time, independence is desired in combinations ofmaterials.

When the known and conventional joining methods, as set out above, areevaluated and compared, one arrives at the realization that innovativealternatives can only be achieved by way of an integral andadhesion-based bond.

If it is desired, in addition, to eliminate with certainty the potentialrisk of the physical joining methods, such as, for example, corrosion,the only fastening option left in principle is the integral bond bymeans of adhesive bonding, whereby one would also become independent ofthe material. Since modern adhesive technology offered no transfersolutions, it was necessary to enter entirely new territory indeveloping suitable adhesive coating compositions.

The object and aim of the present invention is to provide one-component,reactive and adhesive coating compositions of this kind which aresuitable for (pre)-treating elements to be connected, preferablyfastening elements, with a handleable, tack-free, activatable film orlayer of adhesive and which are able to create conditions such that theelements treated therewith can be employed and processed in analogy tothe physical joining methods. At the same time the intention is, bymeans of such substitutes, to eliminate these disadvantages and knowndeficiencies which exist with mechanical and/or physical joiningmethods.

Adhesive coating compositions of this kind for fastening elements areessential prerequisites and form the basis for a novel, innovativemanufacturing and assembly system incorporating adhesive fastening withhigh bond qualities and high economy.

The object of the present invention is achieved by using aone-component, reactive and adhesive, optionally one-piece coatingcomposition consisting of

a) one or more chemically setting backbone binders having averagemolecular weights (M_(w)) of between 500 and 250,000, a melting and/orsoftening point of >50° C. and a glass transition temperature (Tg) >-20°C.,

b) one or more component(s) which serve for curing and/or crosslinking

for the (pre)treatment of surfaces of fastening elements with amultifunctional, corrosion-, abrasion- and wear-resistant film or layerof adhesive which is tack-free at temperatures <50° C. and can beactivated by means of energy.

In order to fulfil a range of specific tasks in production, treatment orcoating and/or application, only chemically setting backbone binders aresuitable for the novel coating compositions. The term chemically settingbackbone binders is understood by the person skilled in the art to referto those polymers and resins which are converted by a chemicalconversion reaction into polymers of relatively high molecular weighthaving thermosetting properties.

In accordance with the present invention, the adhesive coatingcompositions are built up on the basis of those chemically settingbackbone binders which possess semisolid to solid aggregate states attemperatures <50° C. and glass transition temperatures of >-20° C. Suchpolymers and/or resins, prior to their curing or crosslinking, havethermoplastic properties, and only after the activation does curing orcrosslinking take place, by addition polymerization, polyaddition and/orpolycondensation, to form thermosetting structural polymers of highmolecular weight. Moreover, chemically setting backbone binders suitablefor the novel coating compositions must be able to be cured orcrosslinked by means of energy, so that they are able, alone or withother reactants, to form structural adhesive layers having thermosettingproperties. The average molecular weights (M_(w)) of the backbonebinders and of the other customary polymeric additives are between 500and 250,000.

In order, then, to obtain adhesive coating compositions which can beused to produce multifunctional films or layers of adhesive on thesurfaces of fastening elements, backbone binders are required which canbe cured or crosslinked both by polyaddition and by additionpolymerization, as has surprisingly been found. With such backbonebinders it is possible to formulate the novel one-component adhesivecoating compositions and to use them to produce films or layers ofadhesive which by means of energy are

reactivatable and

curable or crosslinkable in one or more stages.

This multifunctionality of the adhesive layer is an essentialrequirement from practice for the adhesive layer in order to enable asufficient functional adhesive strength to be built up and achieved,when working with very short cycle times, directly after the contact andmounting of the fastening element on a support surface.

From the class of the chemically setting backbone binders preference isgiven to those containing at least 2 reactive groups in the molecule.The reactive groups are preferably epoxide groups and/or ethylenicallyunsaturated groups. The backbone binders originate, in particular, fromthe class of epoxy, vinyl ester and/or (meth)acrylic resins. Theseresins may be aliphatic, cycloaliphatic and/or aromatic in nature, withparticular preference being given to aromatic epoxy and/or vinyl esterresins of phenols, o-cresols, bisphenols, fluorene phenols, novolaks,glycidyl isocyanurates and the like, the reason being that suchcompounds, depending on the mode of curing, provide adhesive layershaving high glass transition temperatures and particularly goodresistance to aging, chemicals and heat. Particularly suitable backbonebinders include those epoxy resins based on tetraglycidyldi- and/orpolyamines, for example N,N,N',N'-tetraglycidyl-α,α'-bis(4-aminophenyl)-p-diisopropylbenzene.

The epoxide groups of these backbone binders can be cured or crosslinkedby way of polyaddition and/or addition polymerization.

So that the fully cured thermoset adhesive films are able to withstanddynamic stresses as well, the novel coating compositions can be modifiedwith toughening agents. In accordance with the present inventioncompounds particularly suitable for this purpose are so-called reactiveliquid polymers based on butadienea-crylonitrile copolymers havingterminal carboxyl, epoxide, amino and ethylenically unsaturated groups,such as, for example, Hycar® ATBN 1300×16 and/or reactive plasticizersand diluents based on highly branched aliphatic hydrocarbon epoxides,such as, for example, PERMETHYL® 100 epoxides and/or copolymers preparedtherewith. As a result of their high reactivity, they are boundchemically into the thermosetting adhesive layer matrix.

The term "component(s) which serve(s) for curing or crosslinking" refersto reactants (hardeners) and/or reaction catalysts which are capable ofconverting the backbone binders and any reactive additives into athermoset state and also, if appropriate, of accelerating the chemicalsetting reactions.

Depending on the choice of setting reactions, epoxides and hardeners areemployed with or without accelerator/reaction catalysts, a furtherpossibility being the reaction of epoxide and accelerator/reactioncatalyst without hardeners. Components suitable for this purpose inprinciple are:

Hardeners: primary and secondary amino, amino amide, amino imide,aminoimidazoline, ether methanamine, mercaptan and phenolic OH groups,carboxylic acids and their anhydrides;

Accelerators/reaction catalysts: proton donors and/or electron-pairdonors, such as protic and/or Lewis acids, acid catalysts, such asp-toluenesulfonic acid, dinonylnaphthalenedisulfonic acid,dodecylbenzenesulfonic acid, phosphorus acids, carboxylic acids,free-radical initiators.

For the desired rapid initial or full curing, especially for multistagecuring or crosslinking, the hardeners and/or accelerators are lesssuitable, especially when employed alone. Substances suitable forachieving short initial and/or full curing times are preferably boronhalide complexes, such as boron trifluoride amines and metal complexesof the general formula

    ML.sub.x B.sub.y or M(SR).sub.x B.sub.z

in which

M=a metal ion

L=a ligand

SR=an acid radical ion

B=a Lewis base

x=a number from 1 to 8

y=a number from 1 to 5

z=a number from 7 to 8.

Metal complex compounds of this kind, containing in particular the ionsof main groups 2 and 3 and of the subgroup elements of the PeriodicTable, ligands of chelate-forming compounds, acid radical ions of aninorganic acid, and Lewis bases, especially imidazole derivatives, aredescribed in the PCT Application WO 91/13925, to which express referenceis made.

Particular preference is given to complexes of the general formula

    M(SR).sub.x B.sub.z

in which M, SR, B, x and z are as defined above, and, surprisingly, tothe combination of aromatic amines and Lewis acids, preferablyarylsulfonic acids.

For the curing or crosslinking of ethylenically unsaturated groups,compounds which form free radicals are required. Suitable such compoundsare organic peroxides, for example benzoyl peroxide, cumenehydroperoxide, ketone peroxide, alone or in conjunction withaccelerators, for example N,N,diethylaniline, toluidines.

It is a further advantage of the complexes of the general formula

    M(SR).sub.x B.sub.z

that they activate both epoxide groups and ethylenically unsaturatedgroups. This enables rapid curing or cross-linking of dual-curingbackbone binders with only one curing catalyst.

The curing or crosslinking of the reactive groups can also be carriedout using radiation. When UV rays are used, photoinitiators and, ifdesired, synergists as well must be added to the novel adhesive coatingcompositions. In the case of ionic curing reactions, it is possible toemploy the abovementioned accelerators and catalysts, for example Lewisbases and Lewis acids. In the case of free-radical curing mechanisms,photoinitiators, for example benzil dimethyl ketal, and, optionally,synergists, for example 4-dimethylaminobenzoic acid, are required.

For electron beam curing no additives are necessary.

The novel coating compositions can be modified by means of furtheradditives. Suitable additives include inorganic and/or organic fillers,reinforcing fibers, pigments, dyes, thixotropic agents, wetting agents,adhesion promoters, and the viscoplasticizing reactive substances(toughening agents) described above.

By means of a careful selection of the curing systems and/or of thecomponents which serve for curing, influence is exerted over

the response temperatures or activation temperatures and curing rates,and

the end properties which can be achieved, especially the structuralstrengths,

of the novel coating compositions and their adhesive layers. In order,then, to enable operation with cycle times analogous to those for thephysical joining methods, with the fastening elements treated with anadhesive layer, it is advantageous, as has surprisingly been found, toemploy dual curing systems. The term dual and/or multifunctional curingsystems refers, in accordance with the present invention, to

a) chemical setting by polyaddition, ionic addition polymerizationand/or

b) single- and multistage curing or crosslinking with the supply ofenergy.

The initiation of the curing reactions or chemical setting reactions inthe novel compositions and their adhesive layers takes place at responsetemperatures or activation temperatures of >80° C., which, consequently,are also the curing and/or crosslinking temperatures.

The response or activation temperatures can be adjusted within widetemperature ranges, and are preferably between 80 and 250° C. The curingrates are not determined solely by the response and activationtemperatures but additionally by further rises in temperature by meansof the supply of energy. Rising temperatures increase the curing ratesand reduce the curing times of the novel adhesive layers considerably.

Another significant parameter is the time-dependent development andbuildup of a functional strength with the novel coating compositions andtheir adhesive layers. This requirement from practice is placed purelyon economic grounds. The term "functional strength" refers to thenecessary initial adhesive strength in the case of bonded pairs ofjoined components so that they can be subjected to further operations inthe manufacturing process. In general it is ≧10% of the final strength.

The development and buildup of the functional strength is, in the caseof the novel adhesive layers, also a time-dependent andtemperature-dependent curing function. In order to make it possible forthe elements treated with novel adhesive layers to be employed ininnovative production and assembly systems incorporating adhesivebonding and fastening as well, functional strength must be developed inperiods <60 seconds, preferably <15 seconds and, in particular, <10seconds. This can be achieved with the novel adhesive layers, as hassurprisingly been found, by

selecting dual-functional or multifunctional curing systems having lowand/or different response or activation temperatures, and/or

initiating curing at temperatures above the response or activationtemperatures.

The term "multifunctional" adhesive films, which are produced by meansof the novel coating compositions on the surfaces of joining elementsand fastening elements, relates preferably to the curing or crosslinkingtemperatures and times. Since in the field of fastening in particular,especially for production-line assemblies, short initial curing andthrough-curing times are required on economic grounds, this state ofaffairs is a particularly characteristic feature in the selection of thebackbone binders, of the component(s) which serve(s) for curing orcrosslinking and in the case of the compositions of the novel coatingsystems. This becomes particularly evident when "spontaneous" functionalstrengths are required in the application of joining elements andfastening elements.

In order to enable this aim to be achieved with the adhesive layers ofthe novel coating compositions, the adhesive layers are advantageouslyto be treated with a multistage curing system. In manufacturing systemsincorporating adhesive bonding and fastening there is also a requirementfor multifunctional curing systems if it is possible with such systemsto meet changing requirements, for example detachable and/or otheradhesive bonds. The multifunctionality of the novel adhesive layers hasits foundation, additionally, in the fact that in addition to theprincipal function of adhesive bonding they have to take over furtheressential duties, including:

corrosion resistance

abrasion resistance and wear resistance

freedom from tack before and after curing

resistance to temperature, aging and/or chemicals, and/or long-termstability

universal fastening elements independent of the material used.

These requirements are placed on the novel adhesive layers, inparticular, when the joining and fastening elements involved aremass-produced and/or bulk products.

However, the novel adhesive layers also meet further critical parametersas are known from production-line manufacturing and assembly operations.For example, in vehicle construction a high number of joining andfastening elements are already mounted, for production reasons, on theuntreated body. Since at this stage of manufacturing the surfaces of theuntreated body have not yet been cleaned or degreased, the conditionsare not ideal for adhesion. In order, nevertheless, to make it possibleto ensure the required "spontaneous" or "immediate" functionalstrengths, especially in the case of application of the joining orfastening elements by means of robots, the novel adhesive layers mustpossess

high oil and fat absorption and/or binding properties and

at least very high initial curing rates.

Depending on the selection of raw materials, especially in the case ofthe backbone binders and the hardener systems, it is possible with thenovel coating compositions to produce structural adhesive layers whichpossess glass transition temperatures of up to 250° C. and temperatureresistance up to 300° C. after through-curing.

The preparation of the novel coating compositions and the treatment orcoating of the surfaces of joining and fastening elements are carriedout using known techniques. The coating compositions are prepared bypreheating the meltable components to their melting point andhomogeneously mixing the hardener component(s) in the melt at below thereaction response temperature.

If the joining and fastening elements are coated by means of rolling,dipping, spraying and the like, the novel coating compositions areprocessed from their solutions, dispersions and/or melts. This type ofapplication, from a liquid phase, has an important influence on themanner of preparation. For treating mass-produced and/or bulk goods,solutions, melts and/or dispersions are preferred. Melts areparticularly suitable for this purpose since they can be processed in aneco-friendly and industrially hygienic manner.

A coating composition solution is prepared by dissolving the backbonebinders in an appropriate inert organic solvent, for example methylethyl ketone or toluene, and then homogeneously mixing in the otheradditives. The solids content is determined by the processing rheologyand the subsequent layer thickness of the adhesive layer.

In the preparation of aqueous dispersions, the adhesive layers have tobe incorporated by dispersion from their melt into an aqueous phase, forwhich high-speed stirring and mixing tools are required. The use ofdispersants or emulsifiers and, if appropriate, the presence of smallamounts of organic solvents may be very useful in this case. When astable dispersion is present, the remaining substances are mixed in and,if required, incorporated by dispersion.

Such aqueous dispersions are particularly suitable for coating by meansof electrophoretic deposition.

To produce and prepare novel adhesive melt compositions it is possibleto employ heated melt kneading units or screw extruders which operatediscontinuously or continuously. In this case it is necessary to operateat temperatures below the response or activation temperatures with veryshort residence times.

For electrostatic powder coating, in contrast, the constituents of thenovel coating compositions are preferably prepared in a so-calledoscillating single-screw extruder.

The joining and fastening elements to be treated with a novel adhesivelayer can be produced from different materials and in molds. Suitablematerials include metals, plastics, cellulose material, inorganicmaterials and many others. So that the novel coating compositionsprovide optimum wetting of the surfaces of the joining and fasteningelements and adhere to them, these surfaces are cleaned, degreased andsubjected if appropriate to specific surface treatments. These surfacepretreatments can be carried out, inter alia, by means of jets, coronadischarge, low-pressure plasma, erosion. If desired, the pretreatedsurfaces can be provided with adhesion promoters and/or "adhesionprimers" in order to improve adhesion of the adhesive layers, which areto be applied subsequently, to the boundary surfaces.

The treatment and coating of the joining and fastening elements with anovel adhesive layer is carried out in accordance with known techniques,for example by means of

rolling, dipping, nozzle and/or spraying devices from solutions,dispersions and/or melts of the novel coating compositions, airlessspraying being particularly preferred in the case of spray application;

electrophoretic deposition coating from dispersions of the novel coatingcompositions;

electrostatic powder coating from compounded, flowable powder particles.

For the treatment and/or coating of the joining and fastening elementsit is possible in addition to use so-called mixing and metering devices.They offer advantages, especially in the case of highly reactiveadhesive coating compositions, especially when they are employed asmelts. In the case of this technique, the component which serves forcuring or crosslinking is mixed in homogeneously shortly beforeapplication, for example from a nozzle, and the reactive adhesive meltis cooled directly on the adhesive surface to be treated, and is therebyinactivated. Mixing and metering devices of this kind provide for mixingand metering accuracies of about 1 mg.

The adhesive layers prepared from a solution and/or dispersion mustsubsequently be subjected to drying. The adhesive layers produced fromthe melt solidify merely by cooling.

The amount of energy required for coating and/or drying is specific toeach product, in order for the degrees of heating of the novel adhesivelayers to remain below the response temperatures of curing orcrosslinking. In this way it is possible to eliminate instances ofadhesive-layer damage which would have adverse effects, inter alia, inthe development of the functional strengths, as has surprisingly beenfound.

A further subject is the curing or crosslinking of the adhesive layersand the production of structural adhesive bonds between joining andfastening elements and the surfaces of support materials. Thereactivation and curing or crosslinking of the novel adhesive layerstakes place by supplying energy. Depending on the hardener systememployed and on the existing functionalities in the novel adhesivelayers, the energy sources must be capable of providing, in the shortterm, quantities of thermal energy which are able to producetemperatures of between 80 and 350° C. In the case of curing orcrosslinking a distinction must be made between response temperaturesand activation, curing and/or aftercuring temperatures, since these havean influence on the multifunctionality of the adhesive layers. If, forexample, adhesive layers are activated with more functional hardenersystems, then the response or activation temperature is preferably <10°C. below the temperature required for through-curing and/or aftercuring,in order to make it possible to ensure the spontaneous development ofthe functional strength.

Curing or crosslinking can also be carried out in a plurality of stagesif this is required on the part of practice.

The novel adhesive layers can be activated and cured or crosslinkedusing the following preferred types of energy:

thermal energy, such as hot air, steam

radiation energy, such as actinic light, especially UV rays in thewavelength range from 420 to 100 nm;

laser beams;

infrared rays;

electron beams in the low-energy acceleration range from 150 to 300 keVat a dose distribution of from 0.5 to 10 Mrad=from 5 to 100 kGy

high frequency and microwave

ultrasound, especially with magnetostrictive transmitters at frequenciesbetween 2 and 65 kHz

friction and agitation.

In order to reduce the temperature gaps between the existing ambienttemperature and the required response temperature for activating thenovel adhesive layers it is possible to preheat the joining andfastening elements and, if appropriate, the fastening points on thesupport surface as well. These preheating temperatures areadvantageously a few ° C. below the melting and softening points of theadhesive layers. By means of these measures it is possible significantlyto shorten minimum curing times required to obtain functional strengths.

In order to be able to employ efficiently, in innovative manufacturingand assembly systems incorporating adhesive fastening, the joining andfastening elements treated with a novel adhesive layer it is possible,for example, to modify the conditions of known, physical joining methodssuch that they can be employed for activating and curing the noveladhesive layers.

By means of the provision of one-component adhesive or one-piece coatingcompositions according to the present invention, principles,perspectives and preconditions for the (pre)treatment of joining andfastening elements with curable, multifunctional films or layers ofadhesive have been created which can also be integrated into new,innovative manufacturing and assembly systems incorporating adhesivefastening. Since the fastening elements treated with the novel adhesivelayers can be processed in analogy to the known physical joining methodsin the technical field of fastening, a relatively high level of economyin application is also ensured at the same time.

A further essential technical and economic advance is provided by thepresent invention in that

the joining and fastening elements themselves can be manufactured fromdifferent materials and

the joining and fastening elements treated with the novel coatingcompositions are suitable for producing structural adhesive bondsindependent of the material and are thus capable of universalapplication.

Some of the advantages, in dependence on the respective materialcombinations and use conditions, for the joining and fastening elementstreated with the novel adhesive layers, are as follows:

1. Joining and fastening elements

one-component joining and fastening elements treated withenergy-activatable adhesive layers and consisting of differentmaterials, having good stability on storage

tack-free, manageable, abrasion- and wear-resistant adhesive-layersurfaces

stable and high-grade corrosion protection before and after curing

multifunctional adhesive layers with good adhesion to support materials

can be used on greasy and/or oily surfaces

individually adjustable, low response temperatures and rapid curingtimes

early functional adhesive strengths >10% of the final strengths

low-shrinkage and/or no-shrinkage initial curing and through-curing

high tensile strength values up to 25 N/mm²

high breakaway torques, amounting to at least twice those of weldedelements

high temperature resistance (up to 350° C.) and high glass transitiontemperatures (Tg) of up to 250° C.

good aging and/or chemical resistance, and/or-long-term stability

high toughness of the cured adhesive layer.

2. Adhesive bonds

bonding or adhesive fastening of similar and dissimilar materialcombinations

uniform distribution of stresses in the bonded joints, perpendicular tothe direction of loading

no thermal distortion of components

insulating and/or sealing function of the adhesive layer

high dynamic strengths

high vibration damping.

The invention is illustrated by, but not limited to, the examples whichfollow.

EXAMPLE 1

The following adhesive coating composition was prepared:

100 parts by weight (pbw) of N,N,N',N'-tetraglycidyl-α,α'-bis(4'-aminophenyl)-p-diisopropylbenzene, having an epoxy equivalent of 160and a melting point of 65° C., were dissolved in 100 pbw of methyl ethylketone at 25° C. Subsequently, 60 pbw ofα,α'-bis(4-aminophenyl)-p-diisopropylbenzene as hardener and 0.8 pbw ofdodecylbenzenesulfonic acid as catalyst were added to and homogeneouslydissolved in this backbone binder solution. To build up a heat-resistantthixotropic and to reinforce the adhesive coating composition, 1.0 pbwof aramid fiber pulp was incorporated into the composition using ahigh-speed dissolver.

The finished adhesive coating composition possessed highly thixotropicproperties.

This coating composition was used to treat steel bolts with an adhesionarea of 112 mm². The solvent was evaporated off in a drying oven. Thethickness of the adhesive layer on the steel surfaces was between 50 and60 μm. Following the evaporation of the solvents, the adhesive layeradhered firmly to the steel substrate and was dry and tack-free.

The adhesive bolts treated with adhesive layer were used to carry outadhesive bonds on a steel panel. Half of the steel surface was degreasedwith acetone and cleaned. The other half remained uncleaned.

5 bolts each were preheated to 60° C. in a drying oven. The steel panelwas preheated on a temperature-regulable hotplate. During adhesivebonding, the surface of the steel panel had a temperature of 180° C.

The preheated steel bolts treated with the adhesive layer were pressedbriefly onto the steel surface which was at 180° C. After 5 seconds, thesteel plate together with the stuck-on bolts was removed from thehotplate and cooled at room temperature. After cooling to 25° C., thetensile strength values were determined. These were on average 300N--based on an adhesive area of 112 mm².

5 more coated steel bolts were bonded--as described above--on a 2ndsteel panel, but with the modification that the adhesive layers werecured at 180° C. for 20 minutes. After cooling this test panel withstuck-on fastening bolts at 25° C., the tensile strengths and thebreakaway torques were determined.

Tensile strength

cleaned adhesive area: 1800 N/112 mm²

uncleaned adhesive area: 1750 N/112 mm²

Breakaway torques on rotation:

cleaned adhesive area: 10 Nm/112 mm²

uncleaned adhesive area: 10 Nm/112 mm²

These strength values demonstrate that the adhesive coating compositionhas a high oil absorption and binding capacity and has virtually noeffect on the adhesive strengths.

EXAMPLE 2

Example 1 was repeated with the modification that the hardener andcatalyst were replaced by a metal complex compound in accordance with WO91/13925 and, in addition, a pre-adduct was added as toughness modifier.The quantity of FeSO₄ (imidazole)₈ complex added was 10 pbw.Furthermore, 20 pbw of a pre-adduct of butadiene-acrylonitrile copolymerhaving terminal amino groups and a highly branched aliphatic hydrocarbonepoxide PERMETHYL 100 Epoxide (1 : 1) were added.

The fastening bolts treated with this adhesive coating composition,following evaporation of the solvent, had dry and tack-free surfaces.

The testing of the coated steel bolts gave the following values:

response temperature: 150° C.

curing time at 210° C.: 60 seconds

tensile strength: 1200 N/112 mm²

breakaway torques: 15-16 Nm/112 mm²

EXAMPLE 3

15 parts by weight of cobalt sulfate (imidazole)₈ complex were added at70-80° C. in the melt to 100 parts by weight of an o-cresol-novolakepoxy resin modified with carboxyl-terminated butadiene-acrylonitrilerubber (epoxide equivalent about 225, softening point about 70° C.), andthe mixture was briefly homogenized in an extruder.

This adhesive melt was used to coat the adhesive areas of metal bolts,which were then cooled.

Using these adhesive bolts treated in this way, two-stage curing wascarried out. After a residence time of 10 seconds at 110° C. in the 1ststage, a functional strength of 250 N/112 mm² (tensile strength) wasachieved (elimination of 2 mol of imidazole). Aftercuring for 10 secondsat 210° C. gave a tensile shear strength of 2700 N/mm² and a breakawaytorque of 18-22 N/m.

EXAMPLE 4

100 parts by weight of epoxy resin from Example 3 were admixed in themelt with 50 parts by weight of pyromellitic anhydride (hardener) and 5parts by weight of the metal complex compound (NiSO₄ (methylimidazole)₇complex) and the mixture was homogenized on an extruder. It was thenused to treat the adhesive areas of aluminum bolts. The following valueswere found:

curing temperature (inductive heat): 220° C.

curing time: 6 seconds

tensile strength: 1750 N/112 mm² (material fracture)

breakaway torque: 19-21 Nm (material fracture)

EXAMPLE 5

The epoxy resin of Example 3 was melted at 80° C., 4 parts by weight ofdicyandiamide and 4 parts by weight of the metal complex compound (FeSO₄(imidazole)₈ complex) according to Example 2 were mixed into the melt,and the mixture was homogenized in a single-screw extruder. The steelbolts treated with this mixture gave the following values:

curing time: 18 seconds at 200° C.

tensile strength: 2400 N/112 mm²

breakaway torque: 18-20 Nm

EXAMPLE 6

1 mol of the epoxy resin from Example 3 was reacted with one mole ofacrylic acid at a terminal epoxide group. 2 parts by weight of each ofthe photo-initiators Irgacure® 189 and 652 (manufacturer CIBA-GEIGY)were mixed homogeneously into the melt of this dual-functional backbonebinder obtained in the manner described, having one epoxide group andone acrylic group in the molecule, and this mixture was used to treatmetal bolts. Prior to adhesive bonding, the adhesive layer on the boltswas heated and activated under an 80 W UV lamp and an infrared sourcefor 30 seconds. The bolts with the activated adhesive layer were pressedonto a steel panel. After 2 seconds, the functional strength was foundto be 150 N/112 mm. Subsequently, the bonded pairs of joining parts wereaftercured in a hot oven at 180° C. for 30 minutes, and the followingvalues were found:

tensile strength at 23° C.: 1800 N/112 mm²

tensile strength at 150° C.: 1400 N/112 mm²

tensile strength at -25° C.: 1900 N/112 mm²

EXAMPLE 7

The adhesive coating composition of Example 2 was used to treat 10similar fastening elements, made of a glass fiber-reinforced, partlyaromatic polyamide, with a 50 μm layer of adhesive.

The fastening elements, preheated to 60° C., were bonded to a steelplate at 180° C.

After cooling the test specimen at room temperature it was not possibleto determine any tensile strength values or breakaway torques sincematerial fracture occurred in the plastic.

EXAMPLE 8

Example 1 was repeated with the modification that the epoxy resin wasreplaced by a solid novolak epoxy resin having an epoxy equivalentweight of about 230 and the quantity of hardener was reduced to 50 pbw.Finally, the finished solution of the adhesive coating composition wasdiluted further with methyl ethyl ketone to a dippable viscosity of 50seconds, measured in the 4 mm DIN cup.

In this dipping solution, fastening elements of metal and plastic werecoated by immersion followed by draining and drying at 50° C. 2-folddipping gave an adhesive layer with a thickness of 70 μm.

The fastening elements, bonded at 220° C. and cured for 2 minutes, hadtensile strengths of from 1200 to 1400 N/112 mm² /20° C.

Some of these bonded fastening elements were aftercured at 210° C. for180 minutes. The subsequently determined tensile strengths were from1700 to 1800 N/112 mm² /20° C.

EXAMPLE 9

Test elements of bodywork steel sheet (150×100×0.8 mm) were treatedalong the lengthwise edge with the adhesive from Example 3 in a width of120 mm and a thickness of 100 μm.

Uncoated test elements were placed on the cleaned adhesive areas of theadhesive-treated test elements, and, with heating, both areal and spotadhesive bonds were produced.

The areal adhesive bonds were produced in a heated press (200° C.) witha residence period of 30 seconds. The spot adhesive bonds were producedby pressing the overlapping adhesive areas together using tongs, fittedwith heatable pressing jaws (.O slashed. 120 mm), at a temperature of300° C. for 40 seconds.

Some of the bonded test specimens were aftercured at 180° C. for 30minutes. After cooling, the bonded composite elements were used toproduce test specimens each having an adhesive area of 250×120 mm.

The following tensile shear strength values (DIN 53 281-T 02-79-A) werefound: (average values of 5 measurements in each case)

    ______________________________________                                                 Functional strength                                                                        Final strength                                                   N/mm.sup.2   N/mm.sup.2                                              ______________________________________                                        Areal bond 11 (after 30 sec./                                                                           35 (30 min/180° C.)                                     200° C.)                                                    Spot bond  10 (after 40 sec./                                                                           32 (30 min/180° C.)                                     300° C.)                                                    ______________________________________                                    

What is claimed is:
 1. A one-component thermosetting coating compositionconsisting of at least one chemically setting binder, at least onecuring or crosslinking agent, and at least onesaid composition beingsemisolid and tackfree at temperatures <50° C., wherein the chemicallysetting binder has a weight average molecular weight (M_(w)) of between500 and 250,000, a melting point of more than 50° C., a glass transitiontemperature of more than -20° C. and cures fully at a temperature in therange from 80 to 250° C. and in doing so reaches at least 10% of thefinal strength within 15 seconds, the binder has epoxide groups orethylenically unsaturated groups as reactive groups and is capable ofbeing cured or crosslinked to form a thermosetting polymer, wherein thetoughening substance is a polymer selected from the group consisting ofbutadiene-acrylonitrile copolymers having terminal carboxyl, epoxide,amino and ethylenically unsaturated groups, and highly branchedaliphatic hydrocarbon epoxides, and which polymer is reactive so as tobe chemically bound into the binder, wherein at the least one curing orcrosslinking agent is a metal complex of the general formula M(SR)_(x)B_(z) in which M=a metal ion, SR=an acid radical ion, B=a Lewis Base,x=a number from 1 to 8 and z=a number from 7 to 8and said curing orcrosslinking agent is effective to convert said binder to a thermosetstate upon the application of energy to said composition.
 2. Aone-component thermosetting coating composition consisting of at leastone chemically setting binder, at least one curing or cross-linkingagent, at least one toughening agent, and at least one additive,saidcomposition being semisolid and tackfree at temperatures <50° C.,wherein the chemically setting binder has a weight average molecularweight (M_(w)) of between 500 and 250,000, a melting point of more than50° C., a glass transition temperature of more than -20° C. and curesfully at a temperature in the range from 80 to 250° C. and in doing soreaches at least 10% of the final strength within 15 seconds, the binderhas epoxide groups or ethylenically unsaturated groups as reactivegroups and is capable of being cured or crosslinked to form athermosetting polymer, wherein the toughening substance is a polymerselected from the group consisting of butadiene-acrylonitrile copolymershaving terminal carboxyl, epoxide, amino and ethylenically unsaturatedgroups and highly branched aliphatic hydrocarbon epoxides, which polymeris reactive so as to be chemically bound into the binder, wherein at thecuring or crosslinking agent is a metal complex of the general formulaM(SR)_(x) B_(z) in which M=a metal ion, SR=an acid radical ion, B=aLewis Base, x=a number from 1 to 8 and z=a number from 7 to 8and saidcuring or crosslinking agent is effective to convert said binder to athermoset state upon the application of energy to said composition, andwherein said additive is selected from the group consisting of inorganicfillers, organic fillers, reinforcing fibers, pigments, dyes,thixotropic agents, welting agents, and adhesion promoters.
 3. A onecomponent fast thermosetting adhesive composition for fastening elementsconsisting of at least one chemically setting binder, at least onecuring or crosslinking agent, at least one toughening agent and one ormore additives selected from the group consisting of inorganic fillers,organic fillers, reinforcing fibers, pigments, dyes, thixotropic agents,wetting agents, and adhesion promoters,wherein the binder has a weightaverage molecular weight between 500 and 250,000, a melting point ofmore than 50° C., a glass transition temperature of more than -20° C.and cures completely at temperatures in the range from 80 to 250° C. andachieve thereby at least 10% of the final strength within 15 seconds,wherein the binder has epoxy groups, ethylenically unsaturated groups,or both, as reactive groups, wherein the toughening agent is selectedfrom the group consisting of butadiene-acrylonitrile copolymers havingterminal carboxyl, epoxy, amino and ethylenically unsaturated groups,and highly branched aliphatic hydrocarbon epoxides, wherein the binderand toughening agents are combined in such manner that the compositioncontains epoxy and ethylenically unsaturated groups, and wherein thecuring or crosslinking agent is of the group of metal complexes of theformula M(SR)_(x) B_(z), in which M=a metal ion, SR=an acid radical ion,B=a Lewis Base, x=a number from 1 to 8 and z=a number from 7 to
 8. 4. Anarticle of manufacture comprising an element fastened to a surface bythe adhesive composition of claim
 3. 5. The composition of claim 3,wherein the composition is dispersed into an aqueous phase or is inparticle form.
 6. A fastening method comprising surface treating asurface of one object to be fastened to another, and applying thecomposition of claim 3 to the resulting treated surface.
 7. An articleof manufacture which comprises the adhesive compositions of claim 3coated on an element formed of a material selected from the groupconsisting of textiles, plastics, and metals or other inorganicmaterials.
 8. The composition of claim 3, wherein the binder and thetoughening agent are reacted with each other to form a polymer withethylenically unsaturated groups and expoxy groups.
 9. The article ofclaim 7, prepared by a method comprising heating a surface of theelement to a temperature at least as high as the curing temperature ofthe binder and pressing the coated element onto the heated surface.